As a result of a recent request for the improvement in the performance of a semiconductor device, a process (flip chip method, direct chip attach method or the like) for mounting a semiconductor element on a mother board or daughter board having an interconnection circuit formed thereon has attracted attentions. Such a process is presumed to overcome the problems derived from the conventionally employed method, for example, a process for mounting a semiconductor element on a mother board or daughter board after forming a contact on a lead frame through a metal wire from a semiconductor device and being packaged.
The device having said semiconductor element mounted on the mother board or daughter board, on which an interconnection circuit has been formed, in a face-down structure is required to meet a tendency to higher integration of a semiconductor device. As one example which can meet such a request, a semiconductor device having a semiconductor element mounted, in a face-down structure, on both sides of an interconnection circuit substrate such as mother board or daughter board is considered.
As the fabrication process of a semiconductor device having a semiconductor element mounted on both sides, a process through the steps as described below can be conceived by way of example. Namely, as illustrated in FIG. 9, after subjecting at least one of one side of an interconnection circuit substrate 1 having an interconnection electrode formed on both sides thereof and a semiconductor element 3 having a connecting electrode portion 2 to flux treatment, the semiconductor element 3 having the connecting electrode portion 2 is mounted at a predetermined position on said one side of the interconnection circuit substrate 1. At the same time, the interconnection electrode on the interconnection circuit substrate 1 and the connecting electrode portion 2 are connected by melting said connecting electrode portion 2, whereby the semiconductor element 3 is fixed onto the interconnection circuit substrate 1 (flip chip bonding+infrared ray reflow). Then, the flux on the interconnection circuit substrate 1 and/or the semiconductor element 3 is washed (flux washing). After a liquid resin material is poured and filled, as illustrated in FIG. 10, in a space between the interconnection circuit substrate 1 and semiconductor element 3, the whole body is heated to cure the liquid resin material, whereby the space portion is encapsulated with the resin. Indicated at numeral 6 in FIG. 10 is an encapsulating resin layer.
On the other side of the interconnection circuit substrate 1, another semiconductor element 3 is mounted in a similar step to that described above. Described specifically, as illustrated in FIG. 11, after subjecting at least one of the other side of the interconnection circuit substrate 1 and the another semiconductor element 3 having a connecting electrode portion 2 to flux treatment, the another semiconductor element 3 is mounted at a predetermined position on the other side of the interconnection circuit substrate 1. At the same time, the interconnection electrode on the other side of the interconnection circuit substrate 1 and the connecting electrode portion 2 are connected by melting the connecting electrode portion 2, whereby the another semiconductor element 3 is fixed onto the interconnection circuit substrate 1 (flip chip bonding +infrared ray reflow). Then, the flux on the other side of the interconnection circuit substrate 1 and/or the semiconductor element 3 is washed (flux washing). After the liquid resin material is poured and filled into a space between the other side of the interconnection circuit substrate 1 and the another semiconductor element 3 as illustrated in FIG. 12, the whole body is heated to cure the liquid resin material, whereby the space portion is encapsulated with the resin. Fabrication of a double-side flip chip mounted type semiconductor device having the semiconductor element 3 mounted on both sides of the interconnection circuit substrate 1 in this manner can be considered.
The above-described process is however accompanied with the problem that it needs many steps, which makes the fabrication very troublesome.